Field
The disclosed embodiments relate to the design of an optical receiver. More specifically, the disclosed embodiments relate to the design of an optical receiver which extracts an embedded DC signal level from a photocurrent input to provide a reference voltage for the optical receiver.
Related Art
Silicon photonics is a promising new technology that can potentially provide large communication bandwidth, low latency and low power consumption for inter-chip and intra-chip communications. In order to achieve low-latency, high-bandwidth optical connectivity, designs for a variety of optical components need to be developed, including: optical modulators, optical multiplexers/demultiplexers and optical receivers.
The development of high-performance optical receivers presents a number of design challenges. During operation, an optical receiver obtains a photocurrent from a photo detector, and converts it into an amplified voltage signal. During this conversion process, the optical receiver extracts an embedded DC signal level from the photocurrent, and uses this DC signal level as a reference voltage to determine when a high-level signal or a low-level signal is received. Hence, in order to operate properly, the receiver circuitry needs to extract this embedded DC signal accurately. However, this is a challenging task, because due to operational constraints, such as limited physical channel bandwidth and data density, the DC signal level embedded in the photocurrent can change rapidly.
To extract this embedded DC signal, traditional optical receivers often employ a feedback loop that includes multiple high-speed amplifying stages that are part of the optical receiver. This traditional approach has a number of problems. (1) It is difficult to design and verify the feedback loop due to the complex dynamic behavior of the multiple high-speed gain stages. (2) Instability in the feedback loop limits the receiver sensitivity. (More specifically, oscillations caused by the dynamic behavior of the high-speed gain stages can hurt the sensitivity of the optical receiver and can also increase jitter and bit error rate (BER)). (3) Finally, the receiver switching time between low-power (sleep) mode and high-power (operating) mode is quite long because it cannot be smaller than the settling time of the feedback loop.
Hence, what is needed is an optical receiver that is able to extract an embedded DC signal from a received photocurrent without the above-described problems.